0:08Skip to 0 minutes and 8 secondsWe introduce this module by saying that forensic biology can contribute to establishing what, and also how, where, and when in the investigation of crimes against the person, and we'll now look at this in more detail. The obvious conditional statement first. What follows only applies to crimes of violence in which blood has been shed as a result of the assault. And a less obvious but essential consideration, using blood pattern analysis to explore what is at least as much a matter of crime scene investigation as it is of forensic biology. And the quotation we cited before, from Sir Arthur Conan Doyle's Sherlock Holmes novel The Sign Of The Four, A Scandal In Bohemia very much applies here, too.

0:57Skip to 0 minutes and 57 secondsIt is a capital mistake to theorise before one has data. Insensibly, one begins to twist facts to suit theories, instead of theories to suit facts. So what are the facts that will be the basis of our theories as to what happened? First of all, is there blood at the scene, on a weapon, or on the clothing of the suspect? Next, does the physical nature of the shed blood tell us anything about how it got there? For example, could the blood on the clothing of a possible suspect have arisen from that person being in contact with the bleeding victim when evaluating what had happened, or rendering first aid?

1:37Skip to 1 minute and 37 secondsLastly, can we draw any conclusions about the position of the victim when injured? Demonstrating the presence of blood and using its appearance to reconstruct how it got there is usually referred to as blood pattern analysis, or BPA. Apart from the chemical screening step, BPA is essentially about how surface tension, the force of the action that produces the injury, and the nature of the surface on which the shed blood is deposited combine to provide the information on which the reconstruction is based.

Blood pattern analysis

This very short video introduces us to the part that Blood Pattern Analysis can play in investigation of assault.

We are now going to take a look at blood pattern analysis in a little more detail.

Have a look at the two YouTube videos about blood pattern analysis listed in the ‘see also’ resource section below. There is also a tutorial for you to read. These will help you to understand the material in the next section. You might want to watch the videos a few times.